looks like one of the species gladioli but not 100% sure.

Looks like one of the "Baby Gladiolus" (G. x colvillei hybrids) to me.

Thanks for suggestions. I had considered gladiolus, but will investigate further.

It does look like a gladioli - or Dietes?

I'm going with Gladiolus aureus at present. However, I'm a bit doubtful: the plant is South African and not frost-hardy yet stood outside in its pot all through the winter. On the other hand, this is a sheltered, walled garden on the Solway Coast and we only had a couple of mild frosts so maybe it wasn't affected by that.

G. aureus? Hmm...I'm still going with G. x colvillei, probably 'Albus', or a close cousin.